Pedicle screw handling techniques “lead to contamination of screws”

Guarded pedicle screws being used in spine surgery. Courtesy: Spinal Balance

Standard pedicle screw handling techniques lead to contamination of screws and therefore the screw-bone interface, according to the findings of a prospective multicentre study published in the Clinical Spine Surgery Journal. The study’s corresponding author, Aakash Agarwal (University of Toledo, Toledo, USA) writes that this could be avoided through the use of a sterile intraoperative guard (Spinal Balance), preinstalled inside the individually packaged sterile screws, shielding them from contamination until implantation.

According to Agarwal, postoperative infections occur at the higher end of 2–13% of posterior thoracic and lumbar instrumented fusions, and, despite concerns associated with vancomycin application immediately before closure, it is “theoretically impossible” to irrigate the screw-bone interface post-implantation, he writes. Consequently, Agarwal notes, any contamination of the pedicle screw before implantation is permanent and has the potential to cause deep-bone infection, or hardware loosening due to encapsulation of biofilm and the screw.

In order to assess bacterial contamination in current practices Agarwal and colleagues studied pedicle screw handling at five independent hospital groups, comparing it to a novel method utilising an intraoperative, sterile implant guard for screws. Two groups of pre-sterile individually-packaged pedicle screws, one encased with the sterile, protective guard (group 1: G) and the other without such a guard (group 2: NG), comprising 31 samples in each group, were distributed over 28 spinal fusion surgeries at the five institutions and monitored by Agarwal and his team.

During surgery, screws from each group were held and loaded by the scrub tech, and subsequently left on the “sterile” working table. Approximately 20 minutes later, the lead surgeon, who had finished preparing the surgical site, examined the pedicle screw, to check the fit with the insertion device, and, instead of implantation, it was transferred to a sterile container using fresh sterile gloves for bacterial analysis.

Summarising the results, Agarwal writes that the standard unguarded pedicle screws presented bioburden in the range of 105 to 107 colony-forming units per screw, whereas the guarded pedicle screws showed no bioburden.

“The crucial information unmasked here is the presence of bacterial contaminants on pedicle screws when handled using currently accepted ‘sterile’ techniques, that is, without guards,” Agarwal writes in summarising the findings from the study. “These screws then get imbedded into patients with the contaminants in contact with the patient’s bone at the screw-bone interface.”

According to Agarwal, the study has demonstrated that using a guard around the sterile implant, which shields the screw intraoperatively until it is implanted into the patient, significantly decreases bacterial count and growth. “This may not eliminate SSI [surgical site infection] altogether as it is multifactorial in nature, but should be an important precautionary measure against it, or against the subclinical and chronic infections leading to screw loosening and pain.”

Agarwal writes: “This study provides multicentre clinical evidence that standard pedicle screw handling techniques lead to contamination of pedicle screws and thereby the screw-bone interface. This can be avoided by using a sterile intraoperative guard, which can come preinstalled inside the individually packaged sterile screws, thereby shielding the pedicle screws intraoperatively until implantation.”


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